The present invention concerns the impeller of a pump, in particular a sewage pump impeller, the passage of which is required to have a given transmission capacity for passing through solid impurities present in the sewage water.
Such needs are frequently encountered in sewage pumps in which a small volumetric flow has to be pumped at great delivery lift. In order to achieve good efficiency of the pump and a delivery life/volymetric flow graph of advantageous shape, the passage of the pump impeller should be narrow in the flow-technological sense. As was mentioned at the beginning, the sewage pump should have sufficient transmission capacity because the sewage water also contains solid impurities in abundance, such as rags, shredded plastics, etc. In Finland and in most other countries, sewage pumps are required to have at least 80 mm transmission capacity. This is understood to mean that the pump must pass through a spherical body with diameter 80 mm. Therefore, it has not been possible to reduce the size of the passage so far. Moreover, the width of the passage has up to date been constant over the entire periphery.